Improving the chlorine-tolerant ability of polypiperazine-amide nanofiltration membrane by adding NH2-PEG-NH2 in the aqueous phase

A novel polypiperazine-amide nanofiltration (NF) membrane with very high salt rejection was successfully developed in this work. The NF membrane chlorine-tolerant ability were improved greatly after mixing a small amount of α,ω-diamino poly(ethylene glycol) (NH2-PEG-NH2) with piperazine (PIP) in the aqueous phase. The XPS result demonstrated that the polymerization degree of the NF membrane was notably enhanced with the addition of NH2-PEG-NH2. The solute rejections and chlorine tolerance were improved remarkably, while the permeate flux remained almost at the same level. When the NH2-PEG-NH2 (2 kDa) content in the total amine was 1%w/w (0.01%w/v in the aqueous solution), NF membrane performance was optimal. This membrane exhibited a pure water flux (PWF) of 34.9 L m−2 h−1 along with Na2SO4, MgSO4, MgCl2 and NaCl rejections of 99.5%, 99.2%, 90.9% and 58.3% (2000 ppm, 6 bar, 25 °C), respectively. Moreover, the NF membrane performance was maintained after being treated by 14,000 ppm NaClO for 1 h. Therefore, adding a small amount of NH2-PEG-NH2 in the aqueous phase could be considered to be an effective way to improve the polypiperazine-amide NF membrane chlorine-tolerant ability.